Microstructured apparatus for heating a fluid

ABSTRACT

In a microstructure apparatus for heating a fluid with an inner body received in an outer tube, circumferential micro-passages are formed into the inner surface of the outer tube or the outer surface of the inner body so as to form a flow passage which is provided with inlet and outlet flow structures and heating means are incorporated into the inner body for heating the fluid conducted through the micro-structured flow passages.

This is a Continuation-In-Part Application of International Application PCT/EP03/007954 filed Jul. 22, 2003 and claiming the priority of German application 102 34 043.9 filed Jul. 26, 2002.

BACKGROUND OF THE INVENTION

The invention relates to a microstructure apparatus for heating a fluid, comprising an inner tube surrounded by an outer tube and a microstructure formed at the interface between the inner and the outer tubes.

Microstructure apparatus for heating fluids are used particularly for a position-independent condensation-free evaporation of liquids and for continuous flow heating particularly of gases. Preferred areas of utilization are chemical or pharmaceutical processes and generally the chemical engineering field.

It is generally known to heat fluids by way of electric heating elements. This has the advantage that the heat transfer can be controlled rapidly and in a simple manner by controlling the electric power input. In this connection, micro-structure apparatus have the advantage that, because of the principally smaller dimensions, the heat transfer paths are short and a large specific heat transfer surface can be provided such that the volume-based heat transfer can be relatively high.

DE 199 17 521 A1 discloses such a microstructure apparatus including direct and indirect electrical resistance heaters for heating fluids. The microstructure apparatus comprises layers including microwave channels for the passage of a fluid to be heated and layers including electrical heaters. In comparison with a conventional heat exchanger which is not microstructured, a volume-specific increase of the heat transfer of at least the factor 100 is mentioned. The proposed inner structured apparatus however requires several heating elements with dimensions in the micro-range. For designing the microstructure apparatus for larger fluid flows a number of such heating elements are required and that number increases with the flow volume for added capacity. This is necessary particularly if the volume-specific heat transfer capacity of the microstructure apparatus must not be reduced.

It is therefore the object of the present invention to provide a microstructure apparatus for heating fluids which has heating elements that are simple in their design and which, furthermore, does not have the disadvantages incurred with the design of such apparatus for larger fluid flow volumes.

SUMMARY OF THE INVENTION

In a microstructure apparatus for heating a fluid with an inner body received in an outer tube, circumferential micro-passages are formed into the inner surface of the outer tube or the outer surface of the inner body so as to form flow passages which is provided with inlet and outlet structures and healing means are incorporated into the inner body for heating the fluid conducted through the microstructure flow passages.

It is particularly important that a relatively large or macroscopic heating element is used which has operational advantages in comparison with several micro-heating elements, such as comparatively simple handling and low cost and also use advantages, in combination with a microstructure with its advantage of high efficiency in the transfer of heat to a fluid as pointed out earlier.

The materials of which the microstucture apparatus is manufactured are determined mainly by the application for the apparatus. Basically any materials such as ceramics or other inorganic, non-metallic materials, metals, plastics or combinations or compounds of these materials are suitable.

Below the invention will be described in greater detail on the basis of some embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a, 1 b, and 1 c are cross-sectional views of different embodiments of the apparatus according to the invention,

FIG. 2 is a cross-sectional view of an embodiment with fluid inlet and outlet connections arranged centrally opposite each other, and

FIG. 3 is a cross-sectional view of an embodiment with three intermediate tubes disposed between inner and outer tubes.

DESCRIPTION OF THE VARIOUS EMBODIMENTS

The first embodiment, as shown in FIG. 1 a comprises an inner tube 1 or another body with a preferably cylindrical outer surface, an outer tube 2 concentrically surrounding the inner tube 1 and having an inner surface in tight engagement with the inner tube 1. Inlet and outlet connectors 4 for a fluid are provided near the ends of the outer tube 2 and a microstructure 5 is formed in the interface area between the inner and outer tubes providing a volume in the form of a spiral passage extending between the fluid inlet and outlet connectors 4.

The microstructure is essentially encased between the inner and the outer tubes wherein, ideally, the inner and outer tubes are in sealing engagement at the contact areas.

The microstructure 5 is in the embodiment shown in FIG. 1 a in the form of an internal thread formed into the inner surface of the outer tube 2 wherein the tread course forms a channel interconnecting the two fluid inlet and outlet connectors 4. In this case, the remaining areas of the cylindrical inner surface of the outer tube 2 with a diameter corresponding to the outer diameter of the inner tube 1 should sealingly engage the outer surface of the inner tube 1. The seal connections 3 between the inner and the outer tubes 1 and 2 are chemically, mechanically and thermally resistant ring seals disposed at the opposite ends of the outer tube 2. End covers may be provided to retain the seal rings or the tubes may be formed in these areas for example with cylindrical or conical fittings to hold the seal rings in place. Also, cement or solder connections may be provided for that purpose.

The inner tube 1, which is shown in all figures to be longer than the outer tube 2 extends at both ends from the outer tube 2, although this not necessary. This is also true for a body with a cylindrical outer surface which may be used in place of an inner tube 1 as mentioned earlier. The inner tube or such inner body is in all the embodiments directly or indirectly part of a heating structure. As a direct part of a heating structure, the tube or the body is an integral component of a heating device for example in the form of a resistance heating element. As an indirect part, the tube or the body is for example a heat conductor which conducts heat from a separate heater to the fluid to be heated. These may be separate heaters arranged within the inner tube or adaptively connected to the body. As heaters, electric resistance heating elements are considered to be particularly suitable. Alternatively, a heating medium may be conducted through the inner tube for heating the inner tube 1.

FIG. 1 b shows a second embodiment which is different from the first embodiment (FIG. 1 a) only in that the microstructure 5′ is formed as an external thread into the outer surface of the inner tube 1′ (or an inner cylindrical body), wherein the outer tube 2′ has a smooth inner surface in contact with the inner tube 1′. As in the first embodiment connectors 4 are installed in the outer tube 2′. In this case, care has to be taken upon installation that the connectors are accurately positioned so as to be in communication with the microstructure 5′. With an appropriate sizing of the fit between the inner and the outer tube 1′, 2′, the contact surfaces are sealed so that the seals 3 shown in FIG. 1 are not needed.

In a third embodiment as shown in FIG. 1 c, one of the two connections is formed by an open end of the thread-like microstructure passage 5 at one end of the outer tube 2.

Basically, also other embodiments are possible wherein both connections are provided by open ends of the thread-like microstructure passages. Such an arrangement could be miniaturized in a particularly advantageous manner since separate connectors or sealed connections would not be needed.

Such an embodiment could furthermore be used as continuous flow heater installed between two separate fluid volumes. Since, with such an arrangement, no fluid losses could occur by leakages, sealed connections between the inner and outer tubes would also not be necessary. Further uses for embodiments with the thread-like passages open at least at one end of the outer tube would be for example the atomizing of a liquid to a spray or an aerosol or in the gasification or vaporization of a liquid wherein the particular advantage of the microstructure apparatus resides in its particularly sensitive and accurately adjustable flow control capability.

FIG. 2 shows in cross-section another embodiment, which in its configuration—but not in its operation—is similar to the embodiment shown in FIG. 1 a. Also this arrangement comprises essentially an inner tube 1 and an outer tube 2 with a microstructure 5 formed into the inner surface of the outer tube 2 and two connections 4 and again two seal structures 3 at the opposite ends of the outer tube 2. In contrast to the first embodiment, however, the two connections 4 are arranged opposite each other on the outer tube 2, preferably displaced circumferentially by 180°, but arranged axially at the same location. They extend each to an axial groove 6 formed into the inner surface of the outer tube 2 which communicates with the circumferential passages 5 of the microstructure. A fluid to be heated is introduced through one of the connections 4 to the respective axial groove 6 and from there is distributed to the parallel passages of the microstructure 5″ and flow through these passages to the second opposite groove 6 and out through the second connector 4. Depending on the application, one of the connections 4 and a groove 6 can be combined to a connection extending axially over the microstructure 5.

Another embodiment of the microstructure apparatus is shown in FIG. 3. This embodiment is different from the other embodiments in that one or more intermediate tubes 7 are installed between the inner tube 1 (or cylindrical body) and the outer tube 2. All the inner or, respectively, outer surfaces are fitted to the respective adjacent tube surfaces so as to be sealed therewith as in the preceding embodiments except for the cases mentioned above. As shown in FIG. 3, the microstructure apparatus includes for example three intermediate tubes 7, each provided with a microstructure 5 forming at least one thread-like passage and each including an opening 8 extending through the wall of the intermediate tube 7 placing the thread-like passages of adjacent intermediate tubes and the outer or, respectively, inner tubes in communication with each other. All the microstructure passages are arranged by the openings 8 fluidically in series providing for a microstructure flow chain through the apparatus. The connections 4″ shown in FIG. 3 are in communication with the respective ends of the flow chain wherein the preferred flow direction is from the outer to the inner microstructures, that is, counter to the temperature differential in the microstructure apparatus.

The microstructure passages 5 or the microstructure flow chain may be accessed at any location by additional connections. In this way, fluid amounts with an intermediate temperature can be withdrawn or introduced. Applications for such arrangements are present particularly in chemical engineering, wherein certain reactants or catalysts for chemical reactions must be introduced within a narrow temperature range or small fluid amounts with a certain temperature or a temperature profile must be withdrawn for example for an analysis.

Basically, the microstructure apparatus may be conceived as a chemical micro-reactor. Depending on the application, one or more reaction chambers, that is, one or more areas with increased volume of the passages may be provided in the microstructure or microstructure chain. Further, the manufacture of the whole microstructure apparatus or parts thereof, for example the inner, the intermediate or the outer tube of a catalytic material or a coating of the microstructure 5 at the contact areas with the fluid is possible. A further increase in the volume-specific heat transfer capability can be achieved by an increase in the volume-specific heat transfer area in the microstructure 5, for example, by a porous coating or by roughening of the heat transfer surface areas. The porous coating may also consist of a catalyst or the roughened heat transfer area may consist of a catalyst or be coated by a catalyst. In addition, to avoid corrosion and cavitation, the heat transfer surfaces may be provided with a protection layer consisting for example of a chemically resistant plastic or metallic material or with a wear layer of a chemically or physically deposited metal, hard material or ceramic material. 

1. A microstructure apparatus for heating a fluid, comprising an inner body (1) having an outer surface and including a heating structure, an outer tube (2) concentrically surrounding said inner body (1) and having an inner surface in sealing contact with said inner body (1), a microstructure formed in one of the inner surface of the outer tube (2) and the outer surface of the inner body (1) so as to form a fluid flow passage (5) between the inner body (1) and the outer tube (2), and connectors in communication with said fluid flow passage (5) for conducting a fluid to and from said fluid flow passage (5).
 2. A microstructure apparatus according to claim 1, wherein said microstructure is in the form of a groove (5) extending thread-like around the inner body (1).
 3. A microstructure apparatus according to claim 1, wherein said microstructure is a groove (5) formed like an internal thread into the inner surface of the outer tube (2).
 4. A microstructure apparatus according to claim 1, whereby sealing rings (3) are disposed between the inner body (1) and the outer tube (2) at least one end of the outer tube.
 5. A microstructure apparatus according to claim 1, wherein at least a fluid admission connector and a fluid discharge connector are provided at opposite ends of the outer tube (2) and a screw-like flow passage forms the only communications path between the fluid admission and discharge connectors.
 6. A microstructure apparatus according to claim 1, wherein at least one intermediate tube (7) is disposed between the inner body (1) and the outer tube (2) and each intermediate tube (7) is provided with a microstructure forming a screw thread-like passage between the intermediate tube (7) and a radially adjacent tube or body, the passages being in communication with one another by communication openings (8) extending through said intermediate tubes (7) so as to join the flow passages in a series flow arrangement.
 7. A microstructure apparatus according to claim 1, wherein the connectors (4) are in communication with longitudinal fluid inlet and outlet passages (6) extending over the length of the outer tube (2) at radially opposite sides and providing for communication between the circumferential fluid flow passages (5″) and providing for parallel flow arrangement for the circumferential passages between the inlet and outlet passages (6).
 8. A microstructure apparatus according to claim 1, wherein at least one enlarged cross-sectional area is provided in said fluid flow passage forming a reaction chamber between the inlet and outlet connectors (4).
 9. A microstructure apparatus according to claim 1, wherein the channel walls formed by the microstructure flow passages (5) have a rough surface.
 10. A microstructure apparatus according to claim 9, wherein the channel walls are provided with a porous coating.
 11. A microstructure apparatus according to claim 1, wherein the channels formed by said microstructure are provided with a wear-resistant coating.
 12. A microstructure apparatus according to claim 1, wherein the channels formed by said microstructure are provided with a corrosion resistant coating.
 13. A microstructure apparatus according to claim 1, wherein at least parts of the microstructure apparatus consist of a catalytically active material.
 14. A microstructure apparatus according to claim 1, wherein the channels formed by said microstructures 5 are coated with a catalytically active material.
 15. A microstructure apparatus according to claim 1, wherein the heating structure is an electric resistance heating element.
 16. A microstructure apparatus according to claim 15, wherein said inner body (1) is an inner tube and the heating element is arranged in the inner tube.
 17. A microstructure apparatus according to claim 15, wherein the heating element is an integral component of the inner body (1).
 18. A microstructure apparatus according to claim 1, wherein the inner body (1) is in the form of a resistance heating element. 